The invention relates to an arrangement and a method for carrying out surgical laser treatments of the eye.
It is known in the prior art to use so-called femtosecond lasers, i.e. pulsed lasers with pulse durations in the femtosecond range, for ophthalmological surgery, particularly in order to separate tissue structures on or in the eye. For example, femtosecond lasers are used to perform so-called flap cuts, i.e. incisions into the eye from the side in order to produce a small flap which is folded to the side, for example for a LASIK intervention. Femtosecond lasers are also employed in so-called keratoplasty.
Femtosecond lasers previously used in ophthalmological surgery have generally emitted radiation with wavelengths in the IR range or in the visible range of the electromagnetic spectrum.
U.S. Pat. No. 5,984,916 relates to corneal and intraocular laser surgery, employing pulsed laser radiation whose pulse duration lies between 10 fs and 2 ps with a wavelength of about 400 nm upwards.
U.S. Pat. No. 5,656,186 describes a method for determining a suitable pulse duration for processing a very wide variety of materials with pulsed laser radiation. According to this method, the dependency of the threshold for optical penetration of the material on the pulse duration is initially determined experimentally for a given wavelength. In a curve describing the dependency which is found, a point is then determined from which, towards shorter pulse durations, a quadratic dependency of the penetration threshold on the pulse duration no longer applies. The laser processing per se is then carried out with a pulse duration on the other side of this transition point. Pulse durations in the femtosecond and picosecond range are indicated for this.
The method described in U.S. Pat. No. 5,656,186 is intended to be applicable in an extremely wide wavelength range, which covers virtually the entire laser spectrum used in practice. In any event, a wavelength range of from 200 nm to 2 μm is mentioned in this document. As examples of the variety of materials for which the method is intended to be applicable, metals such as gold and aluminium, glass materials but also living tissue are mentioned, in particular the cornea. For laser treatment of the cornea, a wavelength of 770 nm is specifically indicated.